Hyperthermia is the heating of living tissue for therapeutic purposes. Hyperthermia has been used as a method of treating cancer by means of raising the temperature of a tumor locally, or a region of the body in which the tumor is located, or of the whole body. It has long been known that high heat can trigger the natural regression and/or remission of tumors. Because of its effect on cancer cells, hyperthermia may be used as an independent therapy or in conjunction with other cancer therapies, such as radiation, surgery, chemotherapy, and immunotherapy to enhance the effectiveness of these therapeutic modalities. Current hyperthermia techniques used in cancer therapy include regional perfusion with heated fluids, microwave heating, fluid immersion, low frequency (RF) current fields, and ultrasound.
Three of the most common types of currently used hyperthermia techniques involve radio frequency, microwaves and ultrasound. Radio frequency and microwave equipment may be used for local, regional and whole body heating. Ultrasound can also be used for local and regional heating.
Microwave hyperthermia systems have been developed utilizing direct contact microwave waveguide applicators. The depth of penetration of the microwave energy is frequency-dependent, and the penetration is also a function of tissue composition and anatomical structure. The design of the microwave waveguide applicator radiating antenna influences the thermal distribution. In addition, sharp changes in patient contour within the heated area, as in the head and neck region, will have an influence on the thermal distribution.
Multiple microwave applicator systems for hyperthermia application have been previously developed. One such multiple applicator system is a combination of twelve applicators installed inside of three adjacent stacked rings with four applicators in each ring. Since each applicator is powered from an independent power generator, the system operates in the incoherent mode for its operating frequency of 433 MHz. As a result, the overall heating pattern produced by the multiple applicators is a combination of the individual heating patterns produced by each separate applicator. Such an array of multiple microwave applicators has a fixed geometry with no direct contact possible between the patient and the open end of the applicators. Further, the electromagnetic radiation surrounds the area of the patient's body to be treated, heating all healthy tissue within the field of radiation as well as the tumor. This prior art hyperthermia treatment system is capable of operating only in the incoherent mode at single frequency, and it is capable of use only for regional hyperthermia treatment.
In another existing multiple microwave applicator system for hyperthermia treatment, at least eight applicators are provided in an annular phase array system powered from the same generator for operation only in the coherent mode. In the operation of this system, the heating pattern from the annular array of applicators is a result of the super-position of electromagnetic waves from all eight applicators in the system. The electromagnetic field configuration is a convergent cylindrical wave with the electric field within the applicator parallel to the applicator system axis the body of the patient placed within the annular array of applicators. However, the electric field outside the boundary of the applicator is not parallel and will enter and exit the surface of the body at an angle. This can produce overheating in area where the electric field breaks the boundary of the surface of the patient's body. The system is designed for operation with a frequency range of approximately 40 to 100 MHz. As in the other multiple applicator system, the geometry of the applicators in this system is fixed and direct contact modality is possible between the open end of the applicator and the patient only through a thick water pad. The electromagnet energy delivered to the site of the tumor in the body results in heating (radiation) of all the tissues, healthy cells and abnormal or malignant cells, within the 360.degree. annular energy field pattern, unnecessarily heating a considerable amount of healthy tissue. The annular phase array system is limited in that it is not capable of being operated in the incoherent modality and is capable for use only in regional hyperthermia treatment.
A need has thus arisen for a multiple microwave applicator system for hyperthermia treatment with a flexible geometry for altering the field pattern for enhancing the shape of the field and the heating pattern for the treatment area. A need has also arisen for a multiple microwave applicator system to be operated in direct contact modality with the open end of the applicators contacting the patient or contacting the cooling belt surrounding the patient treatment area. A need has also arisen for contouring the applicators and electromagnetic field to the body treatment area for improving the focusing of the heating pattern and reducing radiation leakage. A multiple microwave applicator system operated in the direct contact modality reduces the unnecessary heating of healthy tissue in non-direct modality. A need has also arisen for a multiple applicator system for use in a hyperthermia treatment system capable of being operated in either the coherent or incoherent mode. A need has further arisen for a multiple applicator system for use in hyperthemia treatment that generates an electric field substantially parallel to the contour of the patient body section treated and one that is capable for use in local and regional hyperthermia treatments.